Date: Tue, 20 Jan 2015 15:32:53 -0800 From: Casey Schaufler <casey@...aufler-ca.com> To: James Morris <jmorris@...ei.org>, Ben Hutchings <ben@...adent.org.uk> CC: Alexander Viro <viro@...iv.linux.org.uk>, linux-fsdevel@...r.kernel.org, linux-security-module@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>, 770492@...s.debian.org, Ben Harris <bjh21@....ac.uk>, oss-security@...ts.openwall.com, John Johansen <john.johansen@...onical.com>, Paul Moore <paul@...l-moore.com>, Stephen Smalley <sds@...ho.nsa.gov>, Casey Schaufler <casey@...aufler-ca.com> Subject: Re: [RFC PATCH RESEND] vfs: Move security_inode_killpriv() after permission checks On 1/20/2015 3:17 PM, James Morris wrote: > On Sat, 17 Jan 2015, Ben Hutchings wrote: > >> chown() and write() should clear all privilege attributes on >> a file - setuid, setgid, setcap and any other extended >> privilege attributes. >> >> However, any attributes beyond setuid and setgid are managed by the >> LSM and not directly by the filesystem, so they cannot be set along >> with the other attributes. >> >> Currently we call security_inode_killpriv() in notify_change(), >> but in case of a chown() this is too early - we have not called >> inode_change_ok() or made any filesystem-specific permission/sanity >> checks. >> >> Add a new function setattr_killpriv() which calls >> security_inode_killpriv() if necessary, and change the setattr() >> implementation to call this in each filesystem that supports xattrs. >> This assumes that extended privilege attributes are always stored in >> xattrs. > It'd be useful to get some input from LSM module maintainers on this. I've already chimed in. Clearing the Smack label on a file because someone writes to it makes no sense whatsoever. The same with chown. The Smack label is attached to the object, which is a container of data, not the data itself. Smack labels are Mandatory Access Control labels, not Information labels. If that doesn't mean anything to the reader, check out the P1003.1e/2c (withdrawn) DRAFT. The proposed implementation does not correctly handle either Mandatory Access Control labels or Information labels. The MAC label is *very different* from the setuid bit. > > e.g. doesn't SELinux already handle this via policy directives? > >
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